1. Technical Field
Several aspects of the present invention relate to surface-emitting type semiconductor lasers.
2. Related Art
As applications of surface-emitting type semiconductor lasers have diversified, and the amount of information in optical communications has expanded in recent years, it is desired further to reduce the number of oscillation modes of surface-emitting type semiconductor lasers while achieving a higher output. For example, in the case of a surface-emitting type semiconductor laser having a selectively oxidized region for optical and current confinement (oxide aperture), the number of oscillation modes may be reduced by reducing the diameter of the oxidized aperture.
It is noted that the output of a semiconductor laser increases with an increase in the injection current, and reaches a maximum value (i.e., a rolloff point) at a certain current. This is because, in a semiconductor laser, its gain spectrum shifts with an increase in the device temperature which is caused by injection current, and the gain reaches a maximum at a certain temperature. When the diameter of the oxide aperture of the surface-emitting type semiconductor laser is relatively small, the temperature of the device would readily elevate, and its rolloff point is reached at a relatively low injection current, such that a sufficient output may not be obtained. In this connection, in an attempt to prevent an increase in the device temperature, Japanese laid-open patent application JP-A-2003-86895 describes a method in which a mesa reaching the lateral current confinement region (hereafter referred as current aperture) is formed, and an electrode is directly formed over the mesa. As a result, the distance between a heat generating section and the electrode is shortened, thereby improving the heat radiation efficiency.